Re: option: /<option/i /\w+/ optarg(?) '>'

On Thursday, May 20, 2004 Alexander Farber said:
> Hi,
> 
> why doesn't the question mark in the optarg(?)
> below work as I expect? In the trace I see that
> optarg consumes the ">" character and then the
> option rule fails, since the final ">" is missing.
> 
> Isn't P:RD supposed to backtrack and say 
> "ok, the optarg(?) didn't match anything here"?

Um, why would it do this?  In fact, "optarg" *does* match zero or one times, 
it is "option" that does not match.  This is a simple problem with your 
grammar where you got (exactly...) what you asked for.

As an example, if you change optarg it will be "better":

optarg: /[^\s>]+/

Also, there is more than one way to do it but I don't "like" your first rule 
for option "/<option/" but would prefer '<' 'option' as it is easier to 
maintain.  If the problem is that there should not be a space between '<' and 
'option' than change skip.

But this is not related to your question, this is just me butting into your 
style... ;-)

> 
> Of course the script below works when I change
> the optarg from /\S+/ to /\w+/, but I'm curious,
> why doesn't optarg(?) mean "ZERO or one" here?
> 
> Thank you
> Alex
> 
> #!/usr/bin/perl -w
> 
> use strict;
> use vars qw($parser $text %option);
> use Data::Dumper;
> use Parse::RecDescent;
> $RD_WARN  = 1;
> $RD_HINT  = 1;
> $RD_TRACE = 120;
> $parser = Parse::RecDescent->new(q(
> 
> genfile: chunk(s) /^\Z/
> chunk: option | <error>
> option: /<option/i /\w+/ optarg(?) ">" {
> 	push @{$::option{lc $item[2]}}, $item[-2];
> } 
> optarg: /\S+/
> 
> )) or die 'Bad grammar';
> $text .= $_ while (<DATA>);
> defined $parser->genfile($text) or die 'Bad text';
> print STDERR Data::Dumper->Dump([\%option], [qw(option)]);
> __DATA__
> <option one>
> <option two>
> 


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-- 
 Intel, Corp.
 5000 W. Chandler Blvd.
 Chandler, AZ  85226